During the coming year, we expect to measure the effects of density, sex, maturity and social rank on serum levels of ACTH, gonadotropins, prolactin, growth hormone, and corticosterone using radioimmune assays and appropriate methodology. For this, six populations will be continued for long-term comparisons with computer simulations and to derive values for a number of important parametric determinants of population growth. These will include maturation time, time between litters, pedigrees, mortality and birth rates and others. The influences of these factors on the computer simulation will be studied. Also a number of parameters used in the computer simulation will be varied systematically in order to determine their relative importance. Seasonal factors (photoperiod and temperature) will be studied also. Experiments will continue on the effects of ACTH-opiate receptor systems on population variables such as maturation and reproduction and vice versa. Our basic programs of computer simulations have been completely debugged and have been refined to the point where we have begun experimental manipulations. These will continue and comparisons between these and similar manipulations of experimental populations will be a major part of our program.